Published on December 18th, 2020 | by David Marshall
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Episode 119: The Soom Shale
The Soom Shale is an Ordovician lagerstätte in the Western Cape of South Africa. Whilst it lacks the diversity of organisms seen in other lagerstätten, such as the Burgess Shale or Chengjiang, it more than makes up for it in the fidelity of preservation.
The taphonomic pathway to the fantastic preservation in the Soom Shale is long and complex, reliant not only on local conditions, but also ties into global climatic events. It’s vitally important when interpreting fossils to understand the taphonomy as it provides so much context as to what you can see in fossils and, as equally important, what you can’t.
Joining us for this episode is Prof. Sarah Gabbott, a taphonomist from the University of Leicester, UK.
This is Table mountain – an iconic symbol of South Africa. Its flat top is because the rocks that make it up are horizontal, but also because there is a shale missing from the top which has eroded away leaving the sandstone flanks. That shale is the latest Ordovician Cedarberg Formation and its base is the Soom Shale Member.
The story of the Soom Shale shale starts with this fossil. This was described as the worlds earliest vascular fossil plant in 1986. But with subsequent work, and thanks to Dr Hannes Theron, and Professors Dick Aldridge and Barry Rickards, we now know these are the teeth of conodonts.
As well as complete teeth sets of conodonts many preserve the conodont eyes as large circles of organic material (top right).
This eurypterid is 8cm in length and shows the remarkable preservation of muscle blocks, a spiral food tract and some of these fossils even have their delicate gills preserved so well that it is possible to make physiological conclusions by comparing them with the gills of modern chelicerate analogues.
The team in 1993. Professor Dick Aldridge, Sarah Gabbott (then a first year PhD student), and Dr Hannes Theron
Orthoconic nautoloids covered in brachiopods which hitch-hiked on their shells
In 1994 literally on the last split of the field season, this conodont animal was found. The spikey tooth set is on the right, with the eyes and trunk preserved in bright clay minerals
Muscle fibres in the conodont animal under high magnifciation
The team in the 2000’s. Dr Hannes Theron, Dr Sarah Gabbott, Rowan Whittle (then a PhD student and now at the British Antarctic Survey), and Professor Dick Aldridge
Rowan and Sarah digging hard!
A cluster of bright quartz grains wrapped in algae (black) with a turbidite below.
Huge amount of algal remains.
The most common fossil is called Siphonacis, its identity remains a mystery to this day.
The late Dick Aldridge enjoying a braai after a hard day collecting.
Claire Browning (Eziko Museum Cape Town) undertaking coring for her PhD studies into the Soom Shale sedimentology
The roads in the area are paved with the Soom Shale, how many exquisite are being driven over every day?!
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